I don't think it is as difficult to go OMFS as Ortho. There are a handful of elite programs that are tough to break into...but there are ton of mediocre to bad ones that one can get into with determination and patience. Having said that...
Go medicine. OMFS is way different than the other dental specialties...way different...and if you don't end up matching OMFS you will be doing something completely non surgical... I almost fell into this trap, i destroyed undergrad but simply loathed dental school and couldn't bring myself to excel...i almost got stuck doing something i couldn't stand, but then fate created the nbme...at least in medicine you still have multiple surgery options even if ortho doesn't work out